Siemens Tristar MCC Short Circuit Ratings

[rockman7892]

Does anyone know where I can find the listed short circuit rating for a Siemens Tristar MCC?

The nameplate on the MCC is listed as having a 65kAIC rating however the breakers in the buckets within the MCC are only rated at 25kA and 35kA depending on the MCC and the breakers that were used.

Is it possible through combination testing to end up with a higher rating of 65kAIC for the MCC even when lower rated breakers are used?

 

[jraef]

Yes it is possible for a complete unit to have a higher rating than the individual components in it, as long as it was tested and listed that way. It's called a Series Rating. But to be sure, you would have to look at the specific UL label for the buckets, it's it is required to be on them and is usually on the back plate although it may have ended up obscured by components. If the unit label is missing or if it does not specifically say 65kAIC, you cannot use it in the MCC that way. What happens sometimes is that people order retrofit buckets and pay no attention to that issue (or look the other way because of price). It's also possible that someone bought surplus frame parts and built their own buckets, that happens too, but those are usually more obvious.

Technically though, the overall SC rating of the MCC is degraded to the lowest rated individual unit. So if you have one bucket that is only 25kAIC, the entire MCC cannot be connected to a system with higher AFC than that.

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[dpc]

Is the nameplate referring to the "Short Circuit Rating" or the bus bracing?

If there is a main breaker in the MCC and there are series ratings for the main and all of the feeder breakers, it possible the series rating could be 65 kA, but I think this has to be denoted as a series rating.